Project Summary Iron deficiency (ID) is common in the U.S, causing significant morbidity. The inability to assimilate adequate amounts of dietary iron, due to increased demands (e.g. with excessive menstrual blood loss) or impaired utilization (e.g. iron malabsorption after gastric bypass surgery), frequently underlies ID. Women of child- bearing age, pregnant women, the elderly (in whom achlorhydria is common), and children and adolescents are commonly iron deficient; in these individuals, iron supplementation may be recommended. During pregnancy, anemia is common since dietary iron assimilation is often inadequate to meet iron demands to supply the developing fetus and for expansion of the maternal blood supply; iron supplementation is thus almost universally recommended. Importantly, we recently noted that high dietary iron caused severe copper deficiency, in rats and mice, with pathological consequences. These initial studies utilized supraphysiologic iron levels (>100-fold excess), but a subsequent experiment demonstrated that iron at ~4X above requirements resulted in moderate copper deficiency in rats. ID humans may consume iron at 4 times the RDA from dietary and supplemental sources. It was previously suggested that high-iron intake can antagonize copper, but this has not been validated by rigorous experimentation in animals or humans. This background then provides the rationale for this investigation in which we will test the central hypothesis that consumption of supplemental iron, at levels similar to what ID humans may consume, disrupts copper metabolism with likely pathological outcomes. Notably, copper deficiency mimics ID, as both conditions cause microcytic, hypochromic anemia. Lack of adequate iron impairs erythropoiesis in ID, while impaired iron utilization by developing erythrocytes underlies copper-deficiency anemia. Physicians may recommend higher iron dosing in patients that are refractory to supplemental iron, thus potentiating the copper deficiency. This investigation could change the existing paradigm of iron supplementation, with added copper accelerating resolution of the anemia and also preventing other pathophysiological effects of copper deficiency, including cardiomyopathy, cognitive dysfunction, and impaired immunity. Three specific aims will be pursued. Aim 1 will define the minimum amount of supplemental iron that perturbs copper homeostasis in rats and mice of both sexes. Aim 2 will identify the mechanism(s) by which supplemental iron perturbs copper homeostasis, possibly involving inhibition of intestinal copper transporters. Aim 3 will evaluate the efficacy of Fe + Cu for preventing the copper depletion associated with high-iron intake in preclinical models of human ID. This investigation may establish an argument for adding copper to iron supplements. Consuming extra copper should be without negative physiologic consequence, and could increase the effectiveness of iron supplementation programs, especially since many Americans may have marginal dietary copper intakes. This investigation could serve as a prelude to intervention trials in humans, which would be a logical extension of the experimentation proposed here.